Delta Air Lines domestic planes were taking to the skies again early Monday but a nationwide ground stop due to a "systems outage" caused departure delays and at least 150 cancellations overnight, the airline said.

Delta's website and mobile app as well as airport information screens and computers at the airline's reservation desks were still down as of midnight ET, barring travelers from obtaining information about their flight statuses.

Delta's website was down early Monday after a "systems outage" forced the airline to ground its domestic fleet, causing delays and at least 150 flight cancellations.

"I want to apologize to all of our customers who have been impacted by this frustrating situation,” Delta CEO Ed Bastian said in a statement. “This type of disruption is not acceptable to the Delta family who prides itself on reliability and customer service.

"I also want to thank our employees who are working tirelessly to accommodate our customers," he added.